The present disclosure is directed to a system and method for calibrating a variable valve actuation system and more particularly to a system and method for calibrating a variable valve actuation system for an internal combustion engine.
Fuel efficiency is a concern in the design and operation of an internal combustion engine, such as, for example, a diesel, gasoline, or natural gas engine. Accordingly, a significant amount of research and development work is being directed towards improving the fuel efficiency of an internal combustion engine. Any increase in fuel efficiency will directly translate to a reduction in the fuel costs associated with operating the engine.
One possible approach to improving fuel efficiency involves precisely controlling the flow of gases into and out of the engine. This may be accomplished by modifying the typical engine valve actuation system to provide flexibility in the actuation timing of the intake and exhaust valves. This may allow the flow of gases to and from the engine to be tailored to meet the particular operating conditions of the engine.
The engine valves in an internal combustion engine are typically driven by a cam arrangement that is operatively connected to the crankshaft of the engine. The rotation of the crankshaft results in a corresponding rotation of a cam shaft that drives one or more cam followers. The movement of the cam followers results in the actuation of the engine valves. The shape of the cam lobe governs the timing and duration of the valve actuation.
An engine may, however, include a variable valve actuation system, such as described in U.S. Pat. No. 6,237,551 to Macor et al., issued on May 29, 2001. In this type of system, a cam arrangement is configured to hold the engine valves open for a certain period of time and an auxiliary valve is included to selectively disengage the cam assembly. This allows the engine valves to be closed independently of the actuation timing of the cam assembly and improves the control over valve actuation timing.
The improved control provided by a variable valve actuation system may allow for gains in fuel efficiency. The variable valve actuation system may be operated to selectively implement a variation on the typical diesel or Otto cycle during the operation of the engine. For example, the intake valves may be controlled to implement a xe2x80x9clate intakexe2x80x9d type Miller cycle. In a late intake Miller cycle, the intake valves of the engine are opened for the intake stroke and held open for a portion of the compression stroke of the engine piston.
The implementation of a variation on the conventional valve actuation timing requires precise control over the engine valves. To obtain the gains in fuel efficiency afforded by the selective implementation of a valve actuation variation, the actual opening and closing of the engine valves should occur within a few degrees of crankshaft rotation of the expected opening and closing of the engine valves. Any variation in the actual opening and closing of the engine valves may negate the potential fuel efficiency gains.
However, each valve actuation assembly may have or develop slightly different response characteristics due to manufacturing tolerances, environmental concerns, and/or wear characteristics. In other words, one valve actuation assembly may open or close an engine valve faster or slower than another valve actuation assembly. The different response characteristics of the valve actuation assemblies may result in a decrease in the potential fuel efficiency gain for a particular engine. Accordingly, the effectiveness of a variable valve actuation system may be improved by accounting for different response characteristics in different variable valve assemblies.
The system and method of the present invention solves one or more of the problems set forth above.
One aspect of the present invention is directed to a method of calibrating a variable valve actuation system. An engine valve is moved from a first position where the engine valve blocks a flow of fluid to a second position where the engine valve passes a flow of fluid. A valve actuator is actuated to prevent the engine valve from returning to the first position. A signal is transmitted to cause the valve actuator and to allow the engine valve to return to the first position. The return of the engine valve to the first position is determined. A time parameter indicative of an elapsed time between the transmission of the signal and movement of the engine valve to the first position is determined.
In another aspect, the present invention is directed to an engine valve actuation system. An engine valve is moveable between a first position where the engine valve blocks a flow of fluid and a second position where the engine valve passes a flow of fluid. A spring is engaged with the engine valve and biases the engine valve towards the first position. A valve actuator is selectively operable to prevent the engine valve from returning to the first position. A sensor is configured to provide an indication when the engine valve is at the first position. A controller delivers a control signal to the valve actuator to return the engine valve to the first position and receives the indication from the sensor. The controller determines an elapsed time between the delivery of the signal and movement of the engine valve to the first position.